861551 has 2 divisors, whose sum is σ = 861552. Its totient is φ = 861550.

The previous prime is 861547. The next prime is 861559. The reversal of 861551 is 155168.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 861551 - 2² = 861547 is a prime.

It is a plaindrome in base 12.

It is a self number, because there is not a number n which added to its sum of digits gives 861551.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 861551.

It is not a weakly prime, because it can be changed into another prime (861559) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 430775 + 430776.

It is an arithmetic number, because the mean of its divisors is an integer number (430776).

2⁸⁶¹⁵⁵¹ is an apocalyptic number.

861551 is a deficient number, since it is larger than the sum of its proper divisors (1).

861551 is an equidigital number, since it uses as much as digits as its factorization.

861551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1200, while the sum is 26.

The square root of 861551 is about 928.1977160067. The cubic root of 861551 is about 95.1539884875.

It can be divided in two parts, 86 and 1551, that multiplied together give a triangular number (133386 = T₅₁₆).

The spelling of 861551 in words is "eight hundred sixty-one thousand, five hundred fifty-one".